Peak capacity of solar cells, denoted in Watt-peak (Wp), Kilowatt peak (kWp) or MW peak (MWp), refers to the maximum power the solar cells can deliver under standard conditions – typically referring to conditions of good sunlight. A 1 kWp solar cell can generate power at 1 kW if the DNI (a measure of sunlight) is good.

However, only during short periods during the day, the DNI is at its peak for a 1 kWp solar cell to operate at full capacity. Thus, over the day, a 1 kWp solar cell generates only about 4 kWh.

If we can have sunlight all 24 hours at ideal DNI, a 1 kW solar cell can generate 24 kWh as it will be operating at peak capacity all the time. In fact, if we were to operate solar panels in space, where sunlight is available at all times at close to ideal DNI, a solar cell of 1 kW peak rating operates at close to its peak capacity most or all the time, and could hence generate much higher than 4 kWh

Questions from the curious cat

At what time of the day is the peak generation reached?

The peak generation for solar cells is reached towards noon in most locations on earth.

Does peak capacity have anything to with extent of solar radiation (DNI)?

Peak capacity is based on the inherent properties of the solar cell and does not depend on the amount of sunlight. But peak generation is dependent on the DNI. For the solar cells, peak generation happens during times of good DNI, which is considered to be 1000 W/m2. This amount of DNI happens around noon.

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